It is known that gas-charged liquid components of synthetic resin can be used in the production of foamed or cellular articles in which the gas phase can expand, at least in part, to produce cells or cavities in the body when it sets or hardens.
In the production of foamed polyurethanes, for example, a gas, constituting a foaming agent, can be incorporated in the liquid polyol component which is combined with diisocyanate or polyisocyanate in a mixing chamber to form a reactive mixture which, upon entry into the mold, allows the gas to expand and bring about a foamed structure.
With processes utilizing the two-phase system polyol/air for the production of polyurethane foams, the foaming action is a function of the quantity of air or gas bubbles which are included in the mixture and which derive from air or gas entrained with the polyol component.
The quality of the product depends upon the quantity of air entrained with the polyol component and the constancy of this quantity.
To reliably maintain a given set of quality standards for foamed synthetic articles, it is desirable to be able to determine accurately the degree to which the liquid component is charged with the gas and to hold it constant within a narrow range.
The problem has been attacked by other methods and devices in a generally unsatisfactory manner because monitoring of the gas content is usually performed upon a return of bypassed flow of the gas-entraining component.
A liquid sample is taken from the recycled region at a pressure substantially lower than the pressure in the inlet side or high-pressure side of the device.
The measuring device is of the membrane type and the results must be corrected in accordance with approximations for the specific gas/liquid characteristics of the liquid synthetic-resin component at the high-pressure side.
Apart from the relative imprecision of the measurement, the fact that it is also discontinuous is a paramount disadvantage, not only for the uniformity of the quality characteristics and the stability thereof over long periods, but because of the nonvariability of the gas-charging degree.